The present invention relates to an anti-skid control system for use in an automotive vehicle, and in particular to an anti-skid control system in which the degree of a locking condition of each road-wheel is restricted.
An anti-lock braking device has been developed for reducing the braking distance by the prevention of the locked condition of each road-wheel. In addition, a traction control device also has been developed in order to improve the acceleration performance of the vehicle by preventing the slip upon initiation of a rapid acceleration. In each device, the prevention of the slip between each road-wheel and a road surface is attained by adjusting the braking force, which is to be applied to the road-wheel, taking into consideration the deceleration and the slip rate of the road-wheel, and other factors. Such devices are disclosed, for example, in Japanese Patent Laid-open Prints No. Sho 60-154947 and No. Sho 62-31554 which were published without examination in 1985 and 1987, respectively.
Sometimes upon a jumping motion or a turning motion of the vehicle, the road-wheel may move away from the road surface, which will bring a temporary decrease of the load applied to the road-wheel. In general, as the load of the road-wheel is decreased, the road-wheel is apt to be in a more locked condition. If the foregoing reduction of the load of the road-wheel occurs while the braking pressure is being supplied thereto, the road-wheel is more or less compelled to be in a more locked condition. For the prevention of such situation, immediately upon the load reduction the braking force is set to be reduced. Upon recovery of the load of the road-wheel, the braking force is also increased up to a value which is the same as that when the load reduction occurred. However, the recovery of the braking force requires time, which prolongs of the braking distance. Similar problems will be raised in the traction control device.